1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus having a developing device which develops an electrostatic latent image into a toner image.
2. Description of the Related Art
Typically, a liquid electrophotographic printer forms an electrostatic latent image on a photosensitive medium, such as a photosensitive belt or a photosensitive drum, develops the electrostatic latent image with a developing agent having a predetermined color, and transfers the developed electrostatic latent image onto a recording sheet, thereby obtaining a desired image.
The electrophotographic printer is largely classified into either a liquid or dry electrophotographic printer depending on the type of developing agent that the electrophotographic printer uses. The liquid electrophotographic printer uses a liquid developing agent, which is a liquid carrier mixed with powder toner. The dry electrophotographic printer uses a heterogeneous developing agent, which is a mixture of a powder carrier and powder toner, or a homogeneous developing agent composed of powder toner. The dry electrophotographic printer will be described more fully in the following as an example of the electrophotographic printer, under the assumption that the electrophotographic printer uses toner as a developing agent.
The electrophotographic printer includes a developing device, which turns an electrostatic latent image into a toner image. The developing device is formed as an assembly which can be attached to and detached from a main body of the electrophotographic printer.
FIG. 1 is a front view of a conventional developing device, FIG. 2 is a longitudinal sectional view of the conventional developing device, and FIG. 3 is an enlarged view of a portion of the conventional developing device when a sealing element is separated from a photosensitive drum 9 forming an empty space therebetween.
Referring to FIGS. 1 and 2, the conventional developing device includes a developing roller 12d, which is rotatably supported by a lower frame 15, is in contact with the photosensitive drum 9, and develops an electrostatic latent image formed on the photosensitive drum 9 with toner, a regulating blade 12e, which is installed above the developing roller 12d in a holder 12e1 and regulates the thickness of a toner layer attached on the developing roller 12d, and the sealing element, which is installed at either side of the developing roller 12d or the regulating blade 12e and hermetically seals a space between the developing roller 12d and the regulating blade 12e so that toner is prevented from leaking from inside the conventional developing device.
The sealing element is comprised of a main sealing element S4, which is installed at either end of the developing roller 12d and contacts the surface of the developing roller 12d, and an auxiliary sealing element S7, which is installed on the main sealing element S4. The sealing element is formed of an elastically deformable material such that it is easily deformed when an external force is applied thereto.
When the main sealing element S4 seals the space between the developing roller 12d and the regulating blade 12e, the main and auxiliary sealing elements S4 and S7 contact one side of the regulating blade 12e because the regulating blade 12e is installed in contact with the developing roller 12d. Accordingly, the main sealing element S4 may contact one side of the regulating blade 12e as well as the surface of the developing roller 12d. 
When the main sealing element S4 is installed at either end of the developing roller 12d, it comes into direct contact with a bent portion 12e′, which is an end of the regulating blade 12e, and is pushed in a direction marked by “B” of FIG. 3 by a predetermined distance due to friction therebetween.
During developing an electrostatic latent image formed on the photosensitive drum 9 with toner, the regulating blade 12e moves back and forth in a direction marked by “A” of FIG. 3 to regulate the thickness of a toner layer attached on the surface of the developing roller 12d, and the main sealing element S4 is pushed in the direction marked by “B”. Accordingly, an empty space P is formed between the developing roller 12d and the main sealing element S4. The empty space P may also be formed between the developing roller 12d and the main sealing element S4 due to external shock.
Toner removed from the surface of the developing roller 12d by the regulating blade 12e may be undesirably discharged to the outside of the conventional developing device via the empty space P polluting a corresponding electrophotographic printer or a user's surroundings.